[FEATURE REQUEST] Make behavior on key conflict in where clause compatible with ActiveRecord

[a2ikm]

Currently, Plucky and ActiveRecord generate different queries when calling where clause method twice with the same key, i.g. where(a: 1).where(a: 2).

Plucky generates { :a => { :$in => [1, 2] } }, and it behaves like { :$or => [{ :a => 1 }, { :a => 2 }] }.

require "bundler/inline"

gemfile do
  source "https://rubygems.org"
  gem 'plucky'
end

connection = Mongo::Client.new(["127.0.0.1"], :logger => Logger.new("/dev/null"))
db = connection.use("test").database
collection = db['users']

p Plucky::Query.new(collection).where(a: 1).where(a: 2).criteria_hash
#=> {:a=>{:$in=>[1, 2]}}

On the other hand, ActiveRecord generates "users"."a" = 1 AND "users"."a" = 2, and it returns empty set.

require "bundler/inline"

gemfile do
  source "https://rubygems.org"
  gem "activerecord", "6.1.0"
  gem "sqlite3"
end

require "active_record"

# This connection will do for database-independent bug reports.
ActiveRecord::Base.establish_connection(adapter: "sqlite3", database: ":memory:")
ActiveRecord::Base.logger = Logger.new("/dev/null")

ActiveRecord::Schema.define do
  create_table :users, force: true do |t|
    t.integer :a
  end
end

class User < ActiveRecord::Base
end

puts User.where(a: 1).where(a: 2).to_sql
#=> SELECT "users".* FROM "users" WHERE "users"."a" = 1 AND "users"."a" = 2

These behaviors are opposite and can confuse us when building queries with split scoped or methods. So I request to add an option or something like that to make Plucky's behavior compatible with ActiveRecords' one.